Pulsed photovoltaics

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SWNT Periodic Table
Primary and secondary gap semiconductors
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After R Smalley and B Weisman
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After R Smalley and B Weisman
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Pulsed photovoltaics
Picosecond excitation with continuously tunable
wavelength

• high sensitivity detection even with blocking
  contacts
• high spectral resolution (0.1 nm), high time
  resolution
• spectroscopy of amplitude and dynamics of
  photoresponse

• NdYag with regenerative amplifier 30 ps long
  light pulses80 mJ output energy. 1064 nm, 532
  nm, 355 nm.
• Optical Parameteric Generator/Amplifier
• Tunable continuously from 420 nm to 2300
  nmoutput energy gt 100 µJ

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Pulsed photovoltaics

• Photovoltaic signal induced by picosecond pulses
  is a good spectroscopic observable.
• The spectra we observe depend on nanotube
  coverage on the contacts.
• Use these basic observation to develop a rapid,
  useful spectroscopy tool to study the
  distribution of different nanotubes
  characteristics in a given sample such as band
  gaps, chiralities, etc.

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SWNT Sample
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First results
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First results
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After R Smalley and B Weisman
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Additional results
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Summary of first observations

• No voltage applied, we measured photoinduced
  voltage change between contacts
• Transient voltage change, less than 20 ns long,
  the photoinduced charge on the illuminated
  contact appears to be negative (to be
  double-checked).
• The transient appears to be due to a what is
  effectively a photoinduced dipole that relaxes
  back in a few nanoseconds. However, the strength
  of the transient is wavelength-dependent showing
  bands characteristic of nanotube spectral
  features.
• Further investigation will focus on identifying
  the origin of the photovoltaic response by
  comparing different contact configurations and
  different kinds of nanotube coverage.